(Received 7 December 2006; accepted 19 March 2007; published online 23 June 2007)

Abstract - The dynamics of blood neutrophil acyloxyacyl hydrolase
(AOAH) activity, the appearance of endotoxin (lipopolysaccharide, LPS) in
blood and the role of blood neutrophil AOAH in the severity of Escherichia coli and
endotoxin mastitis were investigated in early postpartum dairy cows
experimentally challenged with either endotoxin (n = 6) or E. coli (n = 6). The AOAH
activity of blood neutrophils started to decrease significantly at post
challenge hours (PCH) 6-24 and 12-24 in the endotoxin and E. coli-challenged
groups, respectively; it returned to pre-challenged values at PCH 48 in both
endotoxin- and E. coli-challenged groups. The cows were classified as moderate and
severe responders according to milk production loss in the non-challenged
quarters at PCH 48. There were no severe responders in the
endotoxin-challenged group. In the E. coli-challenged group, only 1 severe
responder was identified. The pre-challenge neutrophil AOAH activity of the
severe responder was 30% lower than that of moderate responders.
No LPS was detected in the plasma of endotoxin-challenged cows; neither was
it found in the plasma of moderate responders in the E. coli-challenged group at
any PCH. However, at PCH 6, a remarkable amount of LPS was detected in the
plasma of the severe responder from the E. coli-challenged group. Furthermore,
neutrophil AOAH activity was increased by 70% in the severe
responder at PCH 6, but it increased by only 15% in moderate
responders. This was followed by a decreased neutrophil AOAH activity at PCH
12-24 and 24-72 in moderate and severe responders, respectively; the
decreased AOAH activity at those PCH was more pronounced in the severe
responder. The pronounced decreased neutrophil AOAH activity during mastitis
often coincided with extreme leukopenia, neutropenia and a maximal number of
immature neutrophils in the blood. Our results demonstrate that a decrease
in neutrophil AOAH activity results in the appearance of LPS in the blood,
and low blood neutrophil deacylation activity could be considered as a risk
factor for severe clinical coliform mastitis.